In a push to provide ever increasing resolution for electronic cameras, two general approaches have evolved. First, a single sensor chip is used to carry very large pixel arrays. Such single chip approach leads to very expensive chips as the number of pixels increase. A second approach is to develop a multi-chip camera where chips are disposed on a plane and where several sensor chips are butted together. With this multi-chip approach, it is difficult to achieve smooth transitions between chips. Some attempts are made to butt one chip against another chip to minimize the seam where the chips butt together. Such an approach leaves inevitable gaps. Furthermore, replacement of failed chips in such a tight array of chips is nearly impossible. What is needed is a high resolution, large format sensor that can be manufactured inexpensively and repaired as needed.
Scanning type sensors (e.g., push broom type sensors) present special problems when larger areas need to be covered. In aerial photography for example, the movement of a plane may be constant, but objects on the ground to the side of the plane's path appear to move slower (in angular terms) than other objects directly under the plane. Distortions so created become significant, particularly when a larger field of view is to be covered. Although such distortions can be corrected, the corrections takes additional processing.
The trend in aerial photography is to use area sensors and capture periodic snap shots of objects on the ground as the plane flies a fixed course. If these images are taken frequently enough, the differences in movements of where the objects appear are nearly cancelled and sharp, undistorted images result. Although the images have overlapping portions, such overlap is relatively easy to correct.
U.S. Pat. No. 6,163,339 to J. Meunier describes an electronic apparatus including a cartridge that comprises an array of focusing elements each of which has a field of vision intersecting a given area within a visible image. The cartridge further includes an array of optical sensors, each of which is optically associated with a respective one of the focusing elements. Adjacent focusing elements have fields of vision intersecting common portions of the visible image whereby substantially the entirety of the visible image is covered by combined fields of vision of focusing elements. In Meunier, a huge computer is required to compute all the pixel array information in order to reconstruct an full complete image. Meunier requires a collimator, a shutter and a pre focusing element. Meunier uses individual packaged sensors and cooling rods to drain generated heat.
U.S. Pat. No. 7,339,614 to M. Gruber et al. describes a large format digital camera systems that include multiple detector arrays with one or more single lens systems to acquire sub-images of overlapping sub-areas of large area objects. The sub-images are stitched together to form a large format digital, macro-image. Gruber's camera is designed to “capture earth surface” from a plane while the object (i.e., the earth in this case) moves in time as well the plane and for this requires actuators in each perspective center. Gruber uses four perspective centers, with one subsystem per perspective center, to stitch images together.
Given this interest in area sensors, there has developed a trend towards high resolution imagers with extremely large Fields of View. When large Field of View sensors with a high resolution are employed, an aerial photographing plane can operate at higher altitude which is beneficial in hostile situations. Large area sensors allow for instant situation awareness when compared to scanning type sensors that require post scan reconstruction of an image. In this way, scanning type sensors limit imaging flexibility. It is desirable to create large area and multi-spectral sensors that have high resolution, are fast and can be manufactured with reasonable yield.